Engines, for example, auxiliary power units (“APU”), are used in aircraft to provide electrical power and compressed air to various parts therein. When an aircraft is on the ground, its main source of electrical power comes from the APU. In particular, the APU can power the electrical systems, environmental control systems, air drive hydraulic pumps, and the starters for the engines. When an aircraft is in flight, the APU may provide pneumatic and/or electric power to the aircraft.
Typically, the APU is located in the aft section of the aircraft, at or near the tailcone section. The APU may communicate with an opening in the aircraft fuselage to allow exhaust gas from the APU and other components to flow therethrough. In some aircraft, an eductor is mounted between the APU and the fuselage opening. The eductor is configured to provide APU cooling, compartment cooling, oil cooling, and an interface for the dumping of surge bleed control air, and the eductor-cooled gas is either redirected back to the APU or to other components of the aircraft or is exhausted out the fuselage opening. The eductor includes an inlet, an outlet, and a flow path therebetween and may include an oil cooler coupled thereto. Conventionally, the eductor inlet is suitably sized to receive a portion of the APU or other component disposed between the APU and eductor to form a radial gap therebetween. The radial gap may communicate with other components of the aircraft, such as, for example, a bleed air plenum or the oil cooler.
Although conventional eductors are relatively effective for cooling and exhausting gas, they suffer from drawbacks. For example, in some instances, the exhaust gas flows through the eductor in a swirling motion. As a result, the gas may not flow entirely out of the aircraft. In particular, a portion of the exhaust gas may recirculate back into the APU or into the bleed air plenum via the eductor inlet gap. Another portion of the gases may swirl within the eductor, but may not flow out the eductor outlet. In either case, the eductor may not operate properly to cool the desired aircraft components. In the past, devices, such as deswirl vanes, have been placed in the APU exhaust duct upstream of the eductor. However, it has been found that such devices produce a large amount of back pressure to the engine, which may consequently compromise engine performance.
Hence, there is a need for a device that reduces or substantially eliminates swirling of exhaust gas without compromising engine performance. Preferably, an eductor is needed that is simple and inexpensive to implement.